package net.minecraft.network;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.CorruptedFrameException;
import java.util.List;
import org.jetbrains.annotations.Nullable;

/**
 * Counterpart to {@link Varint21LengthFieldPrepender}. Decodes each frame ("packet") by first reading its length and then its data.
 */
public class Varint21FrameDecoder extends ByteToMessageDecoder {
	private static final int MAX_VARINT21_BYTES = 3;
	private final ByteBuf helperBuf = Unpooled.directBuffer(3);
	@Nullable
	private final BandwidthDebugMonitor monitor;

	public Varint21FrameDecoder(@Nullable BandwidthDebugMonitor monitor) {
		this.monitor = monitor;
	}

	@Override
	protected void handlerRemoved0(ChannelHandlerContext channelHandlerContext) {
		this.helperBuf.release();
	}

	private static boolean copyVarint(ByteBuf in, ByteBuf out) {
		for (int i = 0; i < 3; i++) {
			if (!in.isReadable()) {
				return false;
			}

			byte b = in.readByte();
			out.writeByte(b);
			if (!VarInt.hasContinuationBit(b)) {
				return true;
			}
		}

		throw new CorruptedFrameException("length wider than 21-bit");
	}

	@Override
	protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List<Object> list) {
		byteBuf.markReaderIndex();
		this.helperBuf.clear();
		if (!copyVarint(byteBuf, this.helperBuf)) {
			byteBuf.resetReaderIndex();
		} else {
			int i = VarInt.read(this.helperBuf);
			if (byteBuf.readableBytes() < i) {
				byteBuf.resetReaderIndex();
			} else {
				if (this.monitor != null) {
					this.monitor.onReceive(i + VarInt.getByteSize(i));
				}

				list.add(byteBuf.readBytes(i));
			}
		}
	}
}